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Riso GR3750, Shrinking image problem Solved or Masked?

Well, I thought it wise to share this 'success' with you folks. I recently handled a Riso GR3750 which was specifically referred to me with an 'Image shrinking' problem. Some other techs had tried and failed to fix it. The machine was shrinking the image to quarter of its original size on an A4 paper, on master also same size image. There was also irritating noise in the master making unit both while making and loading the master. It was really tricky.

To start with I was armed with both the technical manual and a good working FR3910iu model Riso, so I could easily swap the suspected parts. Interestingly I noticed that apart from 'System board' and the 'Image processing board' which are different, the two models share exactly same mechanical parts. So one by one I swapped the following parts, in each case testing by making a master and printing: The TPH, Write roller, write pulse motor, torque limiter, TPH board, the entire Scanning unit complete with scan motor and flexible cable ....Still nothing, only shrinking image. Finally i replaced the whole SYSTEM PCB, it had a ROM version 5.02, i got from a fellow tech. This made a considerable improvement in the image size and the noise in the master loading unit disappeared. The A4 size text (line) image was restored, EXCEPT that now the image was shrinking exactly by 16mm, therefore cutting the image right in the middle of the print, both in the vertical and sub scan direction. I made sure my timing was proper for the A3 SIZE DRUM. I did all the 'Image elongation and shrinkage' adjustment, as well as the others as recommended by manual, still nothing.

Finally, BREAKTHROUGH was when I removed the drum unit and shifted the switches 3 & 4 on the drum control PCB from OFF to ON positions. I also changed the P-disk position from A3 to A4, I then adjusted the SW2 machine selection HEX from position 'C'...i.e GR3750(A3) LCD Type, to position 'E', for a GR1750(Legal). Manual says 'E' position NOT USED in the GR3750. I power cycled the machine, made master and printed copies. The image was fully restored 100%. I knelt down and thanked my GOD. It was a struggle of over 30 days.

So the question is 'Did I really solve the 'shrinkage' problem or merely 'masked' it? Did I in effect changed this machine's model from GR3750 to GR1750? Come on senior Riso gurus, say something. Thanks in advance.

Re: Riso GR3750, Shrinking image problem Solved or Masked?

Originally Posted by DAG COPIERS & COMPUTERS

Well, I thought it wise to share this 'success' with you folks. I recently handled a Riso GR3750 which was specifically referred to me with an 'Image shrinking' problem. Some other techs had tried and failed to fix it. The machine was shrinking the image to quarter of its original size on an A4 paper, on master also same size image. There was also irritating noise in the master making unit both while making and loading the master. It was really tricky.

To start with I was armed with both the technical manual and a good working FR3910iu model Riso, so I could easily swap the suspected parts. Interestingly I noticed that apart from 'System board' and the 'Image processing board' which are different, the two models share exactly same mechanical parts. So one by one I swapped the following parts, in each case testing by making a master and printing: The TPH, Write roller, write pulse motor, torque limiter, TPH board, the entire Scanning unit complete with scan motor and flexible cable ....Still nothing, only shrinking image. Finally i replaced the whole SYSTEM PCB, it had a ROM version 5.02, i got from a fellow tech. This made a considerable improvement in the image size and the noise in the master loading unit disappeared. The A4 size text (line) image was restored, EXCEPT that now the image was shrinking exactly by 16mm, therefore cutting the image right in the middle of the print, both in the vertical and sub scan direction. I made sure my timing was proper for the A3 SIZE DRUM. I did all the 'Image elongation and shrinkage' adjustment, as well as the others as recommended by manual, still nothing.

Finally, BREAKTHROUGH was when I removed the drum unit and shifted the switches 3 & 4 on the drum control PCB from OFF to ON positions. I also changed the P-disk position from A3 to A4, I then adjusted the SW2 machine selection HEX from position 'C'...i.e GR3750(A3) LCD Type, to position 'E', for a GR1750(Legal). Manual says 'E' position NOT USED in the GR3750. I power cycled the machine, made master and printed copies. The image was fully restored 100%. I knelt down and thanked my GOD. It was a struggle of over 30 days.

So the question is 'Did I really solve the 'shrinkage' problem or merely 'masked' it? Did I in effect changed this machine's model from GR3750 to GR1750? Come on senior Riso gurus, say something. Thanks in advance.

I believe the problem will come back you just need to clean or replaced the write roller, they collect a lot of wax from the master roll and increase or decrease the image, once you clean it it works as new

Re: Riso GR3750, Shrinking image problem Solved or Masked?

Originally Posted by LA TECH

I believe the problem will come back you just need to clean or replaced the write roller, they collect a lot of wax from the master roll and increase or decrease the image, once you clean it it works as new

Thanks LA TECH for your views, as I said earlier in my post, i did change the write roller from a known working one of an FR3910iu and it did not make any difference in image quality. I actually cleaned its own write roller many times, with no joy.

Re: Riso GR3750, Shrinking image problem Solved or Masked?

Originally Posted by DAG COPIERS & COMPUTERS

Did I in effect changed this machine's model from GR3750 to GR1750?

Well, that is unlikely, and here's how to tell:
First of all, I apologize, I don't have my paper size conversion table handy at the moment, so I can't tell you the exact size of original to use. Still, if you make prints from the widest original the scanner can handle and the prints look OK across their entire width (excluding the normal margin deletions), your GR3750 is OK, too.
I don't know how much help this will be, but the U.S. maximum print size for the GR1750 was 8.5X14 inches, and the GR3750 was 11X17 inches. I'm pretty sure the GR3750 and GR3770 were the only machines in the GR line that could do 11X17 inch prints.